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F R Wagner

Publications and source records attributed to F R Wagner.

6 recordsLinked to original sources
PubMed2006

Electron localization function in full-potential representation for crystalline materials.

The electron localization function (ELF) is implemented in the first-principles, all-electron, full-potential local orbital method. This full-potential implementation increases the accuracy with which the ELF can be computed for crystalline materials. Some representative results obtained are presented and compared with the results of other methods. Although for crystal structures with directed bonding only minor differences are found, in simple elemental metals, there are differences in the valence region, which give rise to different ELF topologies.

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PubMed2004

Metal-metal bonding in ScTaN2. A new compound in the system ScN-TaN.

Gray microcrystalline powders of ScTaN(2) were prepared from solid-state reactions of delta-ScN with Ta(3)N(5) powders at T = 1770 K. According to thermal analyses the compound is stable against oxidation by O(2) up to temperatures of T = 800 K. In an Ar atmosphere ScTaN(2) decomposes above T = 1250 K and in a N(2) atmosphere above T = 2000 K under release of N(2) to form delta-ScN and beta-Ta(2)N. The crystal structure (space group P6(3)/mmc, No. 194, a = 305.34(3) pm, c = 1056.85(9) pm, Z = 2) was refined on the basis of X-ray and neutron powder diffraction data. It comprises alternating layers of ScN(6/3) octahedra and trigonal TaN(6/3) prisms, which are also observed in the binary nitrides delta-ScN and theta-TaN, respectively. A small degree of anti-site defects (about 5%) was detected. Only a small solubility of ScN in epsilon-TaN was observed, while the solubility of TaN in delta-ScN is >/=10 mol % at T = 1820 K. ScTaN(2) is a diamagnetic small gap semiconductor or a semimetal, as inferred from magnetization and electrical resistivity measurements, consistent with band structure calculations. Chemical bonding analyses with the COHP method yield significant covalent Ta-Ta interactions. Topological analyses of the electron localization function reveal unexpected Ta-Ta three-center bonding basins within seemingly empty trigonal prisms of the TaN(6/3) layers.

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PubMed2002

Large orbital moments and internal magnetic fields in lithium nitridoferrate(I).

The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In Mössbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum.

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PubMed2001

Li24[MnN3]3N2 and Li5[(Li1-xMnx)N]3, two intermediates in the decomposition path of Li7[MnN4] to Li2[(Li1-xMnx)N]: an experimental and theoretical study.

The crystal structure of Li7[Mn(V)N4] was re-determined. Isolated tetrahedral [Mn(V)N4](7-) ions are arranged with lithium cations to form a superstructure of the CaF2 anti-type (P4bar3n, No. 218, a = 956.0(1) pm, Z = 8). According to measurements of the magnetic susceptibility, the manganese (tetrahedral coordination) is in a d(2) S = 1 state. Thermal treatment of Li7[Mn(V)N4] under argon in the presence of elemental lithium at various temperatures leads to Li24[Mn(III)N3]3N2, Li5[(Li1-xMnx)N]3, and Li2[(Li1-xMn(I)x)N], respectively. Li24[Mn(III)N3]3N2 (P3bar1c, No. 163, a = 582.58(6) pm, c = 1784.1(3) pm, Z = 4/3) crystallizes in a trigonal unit cell, containing slightly, but significantly nonplanar trigonal [MnN3](6-) units with C3v symmetry. Measurements of the magnetic susceptibility reveal a d(4) S = 1 spin-state for the manganese (trigonal coordination). Nonrelativistic spin-polarized DFT calculations with different molecular models lead to the conclusion that restrictions in the Li-N substructure are responsible for the distortion from planarity of the [Mn(III)N3](6-). Li5[(Li1-xMnx)N]3 (x = 0.59(1), P6bar2m, No. 189, a = 635.9(3) pm, c = 381.7(2) pm, Z = 1) is an isotype of Li5[(Li1-xNix)N]3 with manganese in an average oxidation state of about +1.6. The crystal structure is a defect variant of the alpha-Li3N structure type with the transition metal in linear coordination by nitrogen. Li2[(Li1-xMn(I)x)N] (x = 0.67(1), P6/mmm, No. 191, a = 371.25(4) pm, c = 382.12(6) pm, Z = 1) crystallizes in the alpha-Li3N = Li2[LiN] structure with partial substitution of the linearly nitrogen-coordinated Li-species by manganese(I). Measurements of the magnetic susceptibility are consistent with manganese (linear coordination) in a low-spin d(6) S = 1 state.

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